Its not just Duskblade thats the problem....
A lot of AD assassin don't even have to land their full combo. They just proc duskblade and electrocute and thats enough to kill a squishy while still holding onto their ult for a potential second kill.
I've seen Zed ult, miss all his Q and still get the kill just by procing duskblade and electrocute.
It brings down the skill cap for assassins...but hey, with the burst from
, its kinda scary to get in the face of an ADC.